Process for preparing steel for enameling

ABSTRACT

Low carbon steel having less than 0.012% carbon, is prepared for enameling by degreasing and rinsing, then heating the steel to 200* to 800*C. and depositing thereon by vacuum evaporation an alloy of iron with another Group VIII metal such as nickel or cobalt, the nickel or the like being present in the alloy in an amount 1 to 15% and preferably 4 to 8% by weight, balance iron, and being present on the steel in an amount 0.5 to 4 grams per square meter and preferably 1 to 3 grams per square meter. The previous need to pickle the steel between degreasing and enameling is thus eliminated, and the number of steps and the cost of equipment and operation is reduced.

United States Patent 1191 Humbert et al.

[451 Oct. 7, 1975 [54] PROCESS FOR PREPARING STEEL FOR ENAMELING [73] Assignee: Cockerill-Ougre-Providenc et Esprance-longdoz en Abrg Cockerill, Liege, Belgium [22] Filed: May 15, 1973 [21] Appl. No.: 360,608

[52] US. .Cl. 427/250; 29/195; 29/196.l; 29/196.6; 427/319; 427/330; 427/327;

[51] Int. C11 C23C 13/02; 8328 15/04 [58] Field of Search 117/50, 71 M, 70 A, 70 C, 117/107, 53, 49, 129; 29/194, 196.1, 195,

3,385,725 5/1968 Schmeckenbecher 117/50 3,594,214 7/1971 Helwig et al 29/l96.1 X 3,639,177 l/l972 Tedmon, Jr. et al. 117/107 3,798,055 3/1974 Hunt 117/107 Primary ExaminerRalph S. Kendall Assistant ExaminerJ0hn D. Smith Attorney, Agent, or FirmYoung & Thompson [5 7] ABSTRACT Low carbon steel having less than 0.012% carbon, is prepared for enameling by degreasing and rinsing, then heating the steel to 200 to 800C. and depositing thereon by vacuum evaporation an alloy of iron with another Group VIII metal such as nickel or cobalt, the nickel or the like being present in the alloy in an amount 1 to 15% and preferably 4 to 8% by weight, balance. iron, and being present on the steel in an amount 0.5 to 4 grams per square meter and preferably l to 3 grams per square meter. The previous need to pickle the steel between degreasing and enameling is thus eliminated, and the number of steps and the cost of equipment and operation is reduced.

7 Claims, N0 Drawings PROCESS FOR PREPARING STEEL FOR N EL The present inventionrelates toa process for the preparation of .steel strip and sheet for reception of a surface layer of inorganic enamel,

The enameling of steel has of course been practiced for a number of years.. It is known that carbon is a source of trouble in enameling steel and that therefore carbon should be kept-low, particularly when, white enamel is applied directly without a prime coat. For

this purpose,.it is known to heat the steel in a moist hydrogen atmosphere to lowerthe carbon content.

According to the prior art, it has also been necessary to subject the surface of enamelingsteel to a careful preparation which comprises principally degreasing, rinsing and pickling. Pickling involves a series of complicated operations whichof course increase the cost of enameling. Moreover, to pickle,,large quantities of acid are used and it is necessary toprovide costly installations for preventing pollution by the discharge of corrosive solutions. Z

Moreover, to achieve good adherence of the enamel, it is known to provide a nickelcoating on the pickled surface. This coating, which may be chemicallyor electrolytically deposited, is fully effective only if the preceding pickling has removed a, quantity of iron within certain limits. For enameling steel of a particular composition, the adherence of the enamel is diminishedif during pickling the weight of the iron removed is less than a predetermined minimum. On the other hand, surface defects of steel become visible through the enamel if the iron removal during pickling is greater than a predetermined maximum. For direct enameling on steel, without a base, coat, it is knownxtov benecessary to remove from the surface to be enameled, metal of the thickness of at least 3 to 6 microns. This removal must be effected during a period of time which ,is as short as possible but which is compatible withthe time necessary for rinsing andnickel plating. v a

As the pickling and nickel plating baths vary as to composition in the course of the processes of the prior art, it is necessary, in order that the iron .removal will be substantial but constant throughout, that all the variables be controlled. Thus, it is necessary to maintain constant the activity of the baths, byheating, by periodic reagent addition, and bypI-l control. Sothatthe iron removval will be as constant as possible, it is-necessary to control the copper and phosphorus content of the enameling steel within narrow limits: high phosphorus accelerates the speed of dissolution of the iron during pickling, while high copper retards the dissolution of iron.

It is also known in the art that not only the weight of nickel deposited on the enameling steel but also the structure of the deposited nickel is quite important. The deposited nickel should have sufficient porosity to permit oxidation of the subjacent steel, which augments the adhesion of the enamel to the steel.

Thus the prior art is plagued with numerous and substantial drawbacks in this field: it is necessary to pickle, and the pickling solutions are corrosive and polluting. Multiple operations are also necessary, with multiple treatment steps which require high skill for their performance. The equipment is cumbersome, expensive and complicated. Finally, the most careful process control is necessary.

v Accordingly, it is an object of the present invention to provide a process for the preparation of enameling steel, which will be much simpler than those known in the prior art, and which will require no pickling and no close control of the elements that accelerate or retard pickling, such as for example, manganese and phosphorus which accelerate pickling and arsenic and copper which retardlit.

The present invention provides a solution to the problems of the prior art in the form of a process for the preparation of steel sheet and strip for enameling, in which the surface to be enameled is degreased and rinsed, the steel is heated and there is immediately applied a coating which is a binary alloy of iron and another iron group metal, that is, iron and another metal from Group VIII of the periodic arrangement of the elements. Particularly preferred are cobalt and nickel.

' Preferably, the enameling steel is heated to a temperature between 200 and 800C. before coating with the alloy.

According to another preferred characteristic of the invention, the iron and the other metal, such as nickel, are applied such that their proportions vary throughout the depth of the coating, the nickel increasing in concentration from the interface between the enameling steel and the coating, in a direction outward.

The coating has a content of nickel or other nonferrous Group VIII metal, from 1 to 15% by weight, preferably 4 to 8% by weight, balance essentially iron.

, The coating is applied in such quantity that the weightof the nickel or other Group VIII metal is from 0.5. to 4 grams per square meter, preferably 1 to 3 grams per square meter.

The coating is applied directly to the enameling steel, by evaporation under vacuum.

The method of preparing the steel for enameling is quite simplepenameling steel having a carbon content less than 0.012%, preferably about 0.004 to 0.005%, is degreased and rinsed by conventional methods, and thenis heated to a temperature between 200C. and 800C. It is then immediately coated with an iron-base alloy, e.g. iron-nickel, deposited by evaporation under vacuum byconventional vacuum evaporation methods for the deposition of metals and metal alloys. Then the coated steel is formed by pressing to the desired shape, at which time no cracking of the coating occurs. Then enameling with an inorganic enamel is conducted according to any known method, on the formed coated surface of the steel.

If the steel thus prepared for enameling is to be stored or if it is to be enameled only after a lapse of time, then the surface thus prepared for enameling by coating with the iron-base alloy can be given a protective coating, which can be a synthetic resin such as polyvinyl chloride that also serves as a lubricant during subsequent pressing and which of course will be removed before actual enameling. Alternatively, the prepared steel may be coated with a protective and lubricating oil which is eliminated by degreasing and rinsing after forming but before enameling. Also, the steel can be given a temporary protective coating known as a dry film, in the form of a protective and lubricating soap which is also removed after forming but before enameling.

The binary alloy comprising the coating of the pres= ent invention, as indicated above, has a content of the minor metal such as nickel which increases in a direction away from the substrate. Thus, the nickel content can for example be zero at the interface between the substrate and the coating, and can increase to a maxi mum of, say, 25% at the exposed surface of the coating,

the average nickel content being within the ranges 1 given above.

To enable those skilled in this art to practice the invention, the following illustrative examples are given:

EXAMPLE 1 A square steel sheet cm. on a side, 18 gauge, is prepared for enameling and has the following composition: carbon: 0.004%; nitrogen: 0.0015%; phosphorus: 0.012%; manganese: 0.300%; chromium: 0.015%; copper: 0.025%; and sulfur: 0.015%, balance iron. The sheet is degreased and rinsed carefully and no pickling is conducted; and then, by vacuum evaporation from two sources of pure iron and pure nickel, there is deposited an iron-nickel alloy whose total weight is 33 grams per square meter and which consists of 6% by weight of nickel, balance iron. The coating thus contains 2 grams of nickel per square meter. The sheet is then pressed to a cup shape and given a coating of inorganic white enamel by a known method. The enamel has excellent adherence and shows no flaws.

EXAMPLE 2 Example 1 is repeated, except that the sheet is not subjected to press forming. Instead, it is enameled while flat. The sheet is then placed on a flat base having a circular hole therein of 23 mm. diameter, the sheet covering the hole. A weight of 1.5 kg. has on its lower surface a semi-spherical projection whose radius is 10 mm.; and this weight is dropped from a height of 50 cm., coaxially of that 23 mm. hole, onto the sheet whose enameled surface is uppermost. The results of this test are evaluated on a scale from 1 to 5. A rating of 5 corresponds to complete loss of adherence of the enamel, that is, total scaling of the enamel in the impact area. A value of 1 corresponds to excellent adherence, that is, substantially no scaling of the enamel.

Tests performed on a plurality of sheets of enameled steel prepared and tested according to this example, gave values of 1 and 2, which are highly acceptable commercially.

Thus it will be seen that the initially recited objects of the present invention have been achieved: the present invention avoids pickling and eliminates the necessity to control copper and phosphorus content. The

process of the present invention is faster, less expensive, and more reliable than those of the prior art, and in certain cases eliminates the necessity of preparing more than one face of the steel, the other face being treatable by a less expensive process such as aluminum coating. The present invention also has greater flexibility of application and, because it eliminates the need for pickling, is nonpolluting in its nature.

Although the present invention has been described in connection with preferred embodiments, it is to be understood the modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.

Having described our invention, we claim:

1. A process for preparing steel sheet and strip for the direct application of white enamel thereto without a prime coat, which consists in degreasing and rinsing steel sheet or strip having less than 0.012% by weight carbon, heating said rinsed steel at a temperature between 200C. to 800C, and depositing by vacuum evaporation on the steel a binary alloy of iron and a member selected from the group consisting of nickel and cobalt, said alloy having a content from 1 to 15% by weight of said member, balance essentially iron, thereby to avoid the need for pickling the steel before enameling.

2. A process as claimed in claim 1, in which said member is nickel and is present in said alloy in an amount 4 to 8% by weight.

3. A process as claimed in claim 1, in which the concentration of said member in said alloy increases from the interface between the steel and the alloy outward.

4. A process as claimed in claim 1, in which said member is present on said steel in an amount 0.5 to 4 grams per square meter.

5. A process as claimed in claim 1, in which said member is present on said steel in an amount of l to 3 grams per square meter.

6. A process as claimed in claim 1, in which said steel has a carbon content of about 0.004 to 0.005% by weight.

7. A process as claimed in claim 1, and thereafter applying white enamel to said steel without pickling said steel before enameling. 

1. A PROCESS FOR PRERARING STEEL SHEET AND STRIP FOR THE DIRECT APPLICATION OF WHITE ENAMEL THERETO WITHOUT A PRIME COAT, WHICH CONSISTS IN DEGREASING AND RINSING STELL SHEET OR STRIP HAVING LESS THAN 0.012% BY WEIGHT CARBON, HEATING SAID RINSED STEEL AT A TEMPERATURE BETWEEN 200*C TO 800*C, AND DESPOSITING BY VACUUM EVAPORATION ON THE STEEL A BINARY ALLOY OF IRON AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALT, SAID ALLOY HAVING A CONTENT FROM 1 TO 15% BY WEIGHT OF SAID MEMBER, BALANCE ESSENTIALLY IRON, THEREBY TO AVOID THE NEED FOR PICKING THE STEEL BEFORE ENAMELING.
 2. A process as claimed in claim 1, in which said member is nickel and is present in said alloy in an amount 4 to 8% by weight.
 3. A process as claimed in claim 1, in which the concentration of said member in said alloy increases from the interface between the steel and the alloy outward.
 4. A process as claimed in claim 1, in which said member is present on said steel in an amount 0.5 to 4 grams per square meter.
 5. A process as claimed in claim 1, in which said member is present on said steel in an amount of 1 to 3 grams per square meter.
 6. A process as claimed in claim 1, in which said steel has a carbon content of about 0.004 to 0.005% by weight.
 7. A process as claimed in claim 1, and thereafter applying white enamel to said steel without pickling said steel before enameling. 